Air conditioning/heating airflow control method and system

ABSTRACT

Individual zone temperature control sensors in a multiple zone system are monitored by a controller, and when one zone calls, the calling zone is allocated all of the airflow from the HVAC system except for a predetermined minimum that is allocated to the other zones. If all zones have equal priority, then the airflow continues to be supplied to the first calling zone until a temperature condition is satisfied, at which time the full airflow is allocated to a second calling zone and only the predetermined minimum is supplied to the first and all other calling zones. When two or more zones having different priorities, or set point deviations, are calling at the same time, the zone with the highest priority or whose temperature is furthest from a set point will become the single zone that is open and receives all of the air except for the predetermined minimum. Air continues to be supplied to that zone until it has achieved a desired temperature, until a higher priority zone calls, or until another zone is furthest from the set point. In order to provide maximum airflow to single zones according to the method of the invention, duct and outlet sizes must be larger than is necessary for conventional systems in which more than the minimum airflow is simultaneously allocated to multiple zones. Instead of utilizing conventional duct size calculations that assume simultaneous allocation of airflow to multiple zones, the design sizes the ducts in each zone to carry 100% of the system&#39;s airflow less the predetermined minimum.

This application is a continuation of U.S. patent application Ser. No.16/174,650, filed Oct. 30, 2018, and incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a method and system for controllingdistribution of air in a multiple zone air conditioning and/or heatingsystem.

2. Description of Related Art

In a conventional multiple zone heating and air conditioning (HVAV)system with a central controller, distribution of heated or chilled airis controlled by opening and closing dampers or vents in response tosignals or calls received by the central controller from thermostats ortemperature sensors in the respective zones. For example, when thetemperature in a zone is warmer than a preset temperature, chilled airfrom a compressor is allowed to pass into the area through a damper. Thedamper remains open until the temperature has cooled to the presettemperature. In general, each of the zones is independently controlledto receive a portion of the airflow as necessary to maintain the presettemperatures in respective zones. Because each zone normally receives atleast a portion of the total output of the HVAC unit, the ducts anddiffusers or vents are sized to receive less than the total output,based in large part on the relative sizes and configuration of rooms orspaces in the zones,

To ensure that particular zones receive sufficient airflow to maintainthe desired temperature as rapidly as possible even when more than oncezone is below or above the desired temperature, it is known toprioritize the distribution of heated or cooled air, so that a largervolume of cooling or heating air is supplied to zones with higherpriority, The priority can be based on which rooms are more likely to beoccupied at particular predetermined times, on actual occupancy of thezone as determined by sensors, on the relative needs of the occupants(for example, the elderly or infants might be more temperaturesensitive), or on other factors. On the other hand, if the supply ofchilled or warmed air output by the heating or cooling system is greaterthan required by all calling zones, excess air may be dumped by ventedout of the building or to areas that are unoccupied.

U.S. Pat. No. 8,061,417 discloses a simple multiple zone HVAC airflowcontrol scheme in which airflow is reallocated to a priority zonewhenever resources in the priority zone are inadequate to meet demand,but numerous variations of this basic scheme are possible and have beenpreviously proposed in a number of patents and publications.

For example, U.S. Pat. No. 4,830,095 describes a control “sequence” inwhich not just a portion of the total HVAC output, entire output isdiverted to one or more zones based on thermostat calls and assignedpriorities. This is similar to the scheme employed by the presentinvention in that the total HVAC output is allocated to calling orpriority zones, but there is no attempt to limit supply of the totaloutput to a single zone, even if multiple zones are calling and haveidentical priorities, or to sequence the air supply from one callingzone to another even when the zones have equal priority. In the controlscheme of U.S. Pat. No. 4,830,095, air will be supplied to the one ormore zones with highest priority for as long as air supply is called forby the thermostat in the zone. If multiple zones have equal priority,then air is supplied simultaneously to each zone, based on thethermostat calls. Thus, this patent describes a sequence in which thispatent describes a control sequence in which air is initially suppliedto zone 1 upon receiving a thermostat call, by allowing the damper forzone 1 to remain open while the damper to zone 2 is closed, after whichair is supplied to zone 2 upon receiving a thermostat call by openingthe damper to zone 2 and closing the damper to zone 1. Any zones thatare independent will receive air simultaneously based on thermostatcalls or in the absence of priority.

Additional prioritization schemes are disclosed in U.S. Pat. No.4,673,029, in which prioritization is accomplished by disabling thethermostat in one zone and having the thermostat in the other zonecontrol the division of air between the zones, and U.S. Pat. No.4,600,144, which describes anticipated usage-based prioritization inwhich airflow to selected rooms or zones is shut off at intervals duringa 24 hour period to account for daytime and nighttime differences inusage.

In contrast, Japanese Patent Publication No. JPS5743140, discloses a“time division system” flow rate control method in which a set ofdampers or “valves” in one zone is opened while valves in all otherzones are maintained in a closed condition. The zones are sequenced sothat after a predetermined time, the valves for the next zone are openedand those for all other zones, including the first zone, are closed.This is similar to the sequencing provided by the present invention inthat air is distributed to only one zone at a time. However, the controlscheme described in the Japanese publication differs from that of thepresent invention in that (a) the system to which the control scheme isapplied is a variable flow rate system in which the valves are onlyopened by an amount sufficient to maintain a minimum flow rate, and (b)the sequencing is predetermined, i.e., based solely on time division,rather than determined by thermostat calls and/or programmable priority.

The present invention not only involves an HVAC airflow allocationscheme, but also a modified duct and damper design, in which ducts areenlarged to accommodate a larger percentage of the HVAC total output.U.S. Pat. No. 6,964,174 also discloses duct size calculation based on adetermination of expected airflow requirements, but there is no attemptto ensure that each zone can receive maximum system airflow as in thepresent invention. To the contrary, control of the system requiresreduction in airflow to a particular zone, if possible, and dumping tounoccupied zones if an expected zone airflow exceeds its maximumairflow.

By way of additional background, U.S. Pat. No. 7,819,331 discloses“staging” of the conditioning device in a VAV system in which theairflow is varied, i.e., changing the airflow volume in response to theduration and sequence of thermostat calls rather than distributing afixed airflow as in preferred embodiments of the present invention.

Finally, U.S. Pat. No. 4,549,601 discloses a variable volume, multiplezone control system in which dampers in at least one zone are alwaysleft fully open to maintain a minimum static pressure in the system.

In general, the conventional airflow control schemes described abovehave worked well and are widely accepted, even though some challengesexist, including problems related to delivering and returning requiredheating or cooling capacity to rooms in tight home that require lowairflows. While numerous variations based on prioritization have beenproposed, the basic scheme of allocating airflow to whichever zonesrequire airflow or have priority, has not been questioned. It is verysurprising, therefore, to discover a control scheme that alters theconventional allocation scheme and achieves substantial increases inefficiency solely by altering programming of the central controller andby making simple changes in the duct and damper size calculations.

SUMMARY OF THE INVENTION

It is accordingly an objective of the invention to provide an airflowcontrol method and system for multiple zones that achieves substantialimprovements in efficiency without requiring any modifications of theconventional HVAC system other than changes in programming of thecentral controller and modification of duct and damper sizecalculations.

It is also an objective of the invention to provide an airflow controlmethod that solves problems related to delivering and returning requiredheating or cooling energy to rooms in tight homes that require lowairflows.

These objectives, which are not intended to be limiting, are achieved bya control system and method in which each zone is arranged to beallocated a maximum airflow output of the HVAC unit, minus apredetermined minimum that is allocated to zones. During operation ofthe system, only one zone at a time is supplied the full airflow (i.e.,the maximum output less the predetermined minimum), while thepredetermined minimum is allocated to all of the other zones.

According to a preferred embodiment of the system and method of theinvention, initial allocation is by a call from a thermostat or sensorin one of the zones. Once air supply to the initial calling zone hasstarted, the calling zone continues to be supplied with air until adesired set point has been achieved.

Optionally, airflow can be switched from the initial calling zone toanother calling zone based on priority or on deviation of from athermostat or temperature sensor set point. Upon switching to a higherpriority zone, or a zone with a greater deviation from the set point,airflow to the initial zone is reduced to the predetermined minimum andairflow to the second zone is increased to maximum, less thepredetermined minimum. During switching from a first zone to a secondzone, the diffusers in the first zone must be left open until thediffusers in the second zone are fully open, or some other outlet orbypass must be provided to avoid over pressurization.

In order to accommodate the maximum airflow, the invention provides forduct design modifications in which the ducts and diffusers in each zoneare enlarged to accommodate a maximum HVAC unit output, minus a smallairflow necessary to provide adequate minimum ventilation to zones notsupplied with the full airflow. The calculations are modifications of,and can utilize principles described in, conventional HVAC designmanuals such as Manual Zr, Manual T, Manual S, and Manual J.

An optional delay step may be added to the basic airflow control methodto prevent the air conditioning equipment from short cycling, the delaystep preventing the condenser from being restarted until after apredetermined interval if the conditions in a zone are met before theinterval has elapsed from the initial start. In an illustrated example,the delay is five minutes, but the delay interval can be variedaccording to manufacturer requirements for specific equipment.

While the method of the invention is especially suitable for singlespeed systems, it is possible to apply the same design and controlcriteria for multiple or variable speed systems, with full flow to onezone being provided for whenever the system is operated at low speed.

In addition to the advantages listed above in connection with objectivesof the invention, the design sequence and control strategy of theinvention simplification of airflow balancing, lower blower operatingcosts, and improved humidity control by maintaining coil temperature andfan speed at the design values. The method of the invention meets thezone requirements on all days, under all weather conditions because thezones are not proportionally dependent on a single load value, andbecause the method of the invention self-adjusts for the differences inheating and cooling loads for zones. The hardware for implementing themethod and system of the invention is not only commercially available,but is already available from many manufacturers, while the softwareprogramming can easily be accomplished by modifying existing zonecontrol systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of a control and sequencing method for controllingdistribution of airflow in a multiple zone HVAC system according to afirst preferred embodiment of the present invention.

FIG. 2 is a flowchart of an airflow control and sequencing method forcontrolling distribution of airflow in a multiple zone HVAC systemaccording to a second preferred embodiment of the present invention.

FIGS. 3-5 are tables illustrating, by example, duct capacity designprinciples of the preferred embodiments of the invention.

FIG. 6 shows the floor plan for which the values shown in FIGS. 3-5 werecalculated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a multiple zone airflow control method andsystem that directs all air, minus a predetermined minimum, to one zoneat a time. The control system and method of the invention utilizes thefollowing principles:

-   a. Individual zone temperature control sensors or thermostats are    monitored by a controller. When one zone calls by sending a signal    indicative of a difference between sensed temperature and a set    point, the calling zone is allocated all of the airflow output by a    central from the HVAC limit, minus a predetermined minimum that is    allocated to the other zones.-   b. When two or more zones are calling at the same time, the zone    with the highest priority or whose temperature is furthest from a    set point will become the single zone that is open and receives all    of the airflow, minus the predetermined minimum. Air continues to be    supplied to the initial calling zone until it has achieved a desired    temperature, until a higher priority zone calls, or until another    zone calls and is further from the set point than the initial    calling zone.-   c. In order to provide maximum airflow to single zones according to    the method of the invention, duct and outlet sizes must be larger    than is necessary for conventional systems in which more than the    minimum airflow is simultaneously allocated to multiple zones.    Instead of utilizing cooling and heating factor calculation    procedures based on division of total HVAC unit output, the    inventive design sizes the ducts and/or diffusers and return grilles    to carry 100% of the system's airflow less the predetermined    minimum.

The predetermined minimum supplied to the zones other than the callingor priority zone may, by way of example and not limitation, amount to10% of the total airflow. This ensures a minimum air circulation inorder to provide the uniform mixing of outside air that is recommendedfor highly sealed homes, similarly to the minimum airflow required forcommercial variable air volume (VAV) systems. One way to achieve the 10%setting is to arrange the dampers that control the airflow to a zone sothat they cannot be completely shut, but instead have an opening of 10%the maximum opening when in the “closed” position. Alternatively, apercentage of the dampers in a zone may be left in an open position toprovide the necessary ventilation, while the majority of dampers areshut. Those skilled in the art will appreciate that the minimum value of10% may be varied to meet environmental or health requirements withoutdeparting from the scope of the invention.

FIG. 1 is a flowchart illustrating basic control principles of a firstpreferred embodiment of the invention, in which a first-called zone issupplied with maximum air flow, The maximum airflow is defined asairflow to a zone in which the dampers are all open, minus thepredetermined minimum that is supplied to all other zones. Initially, asindicated by block 1, the control system waits for a call from athermostat or temperature sensor in one of the zones, indicating thatthe sensed temperature is above or below a set amount by a predeterminedamount. The arrangement of the thermostat or sensor and the manner inwhich calls are made by the thermostat or sensor and received by thecontroller is conventional. When a call is received, the controllerproceeds to step 2, and opens the dampers in the calling zone to supply100% of a fixed airflow from a central heating or air condition unit tothe zone, minus a predetermined minimum as described above. Dampers ineach of the non-calling zones remain shut to only permit thepredetermined minimum airflow.

The controller continues to supply air to the current calling zone untilthe current zone is satisfied, i.e., the set point has been achieved, asdetermined at step 3, at which time the controller will shut off themaximum air supply to the current zone and return to step 1, in which aminimum airflow is supplied to all zones. If a second zone has called,as determined at step 2, then the maximum airflow is supplied to thesecond zone until the second zone is satisfied, at which time thecontrol system switches the next zone to call.

An optional delay step 5 may be inserted to prevent the air conditioningequipment from short cycling, a delay may be included to prevent thecondenser from being restarted until after a predetermined interval ifthe conditions in a zone are met before the interval has elapsed fromthe initial start. The delay may be five minutes, but this delay canvary according to manufacture requirements for specific equipment.

FIG. 2 is a flowchart illustrating the basic control principles of asecond preferred embodiment of the present invention, which provides forswitching of the maximum airflow from a first zone to a second zonebefore the first zone has been satisfied, based on priority or deviationin temperature from a set point. Initially, in step 10, the systemsupplies a minimum airflow to all zones, and the control system waitsfor a call from a thermostat or temperature sensor in one of the zones,indicating that the sensed temperature is above or below a set amount,as determined in step 11. As with the first embodiment, the arrangementof the thermostat or sensor and the manner in which calls are made bythe thermostat or sensor and received by the controller in thisembodiment are conventional.

When a sensor call is received, the controller proceeds to step 12, andopens the dampers in the calling zone to supply 100% of a fixed airflowfrom a central heating or air conditioning unit to the zone, minus apredetermined minimum as described above. Dampers in each of thenon-calling zones remain shut to only permit the predetermined minimumairflow.

When a call is received from a zone other than the one currently beingsupplied with maximum airflow, as determined at step 13, the controllerchecks the priority of the zone or, alternatively, whether the zone isfurther from the set temperature than the zone currently being supplied,as determined at step 14. If another zone has not called, or does nothave a higher priority or distance from the set point, the controllercontinues to supply air to the current calling zone until the currentzone is satisfied, i.e., the set point has been achieved, as determinedat step 15, at which time the controller will shut off the maximum airsupply to the current zone.

As described above in connection with FIG. 1, an optional delay step 16may be inserted to prevent the condenser from being restarted untilafter a predetermined interval if the conditions in a zone are metbefore the interval has elapsed from the initial start.

If the controller determines at step 14 that a second calling zone doeshave a higher priority or is further from the set point, then thecontroller will first fully open the second calling zone to the maximumairflow position before shutting off the maximum air flow to the firstcalling zone, as indicated by step 17, in order to accomplish aswitchover or shift between zones. Shifting between zones is thusaccomplished by permitting dampers in an open zone to remain open untilthe next zone is able to receive the full airflow in order to avoid overpressurization of the duct system.

If priority rather than set point deviation is used as the basis fordetermining which zone is allocated the maximum airflow, then thepriority may be set by a user according to specific needs. For example,the suite of an elderly person or infant can be set to always havepriority over other zones. The priority could also be based onoccupancy, time of day, nature of the zone, or any other basis fordetermining which zone should be first to receive heating or coolingairflow following a function call. In addition, priority levels can becombined so that, for example, the suite of an elderly person or infantcan be accorded the highest priority when occupied, and a lower prioritywhen unoccupied.

Although the present invention can be applied to any multiple zone HVACsystem, a smaller number of larger zones make the system simpler andmore efficient to operate that a large number of smaller zones. Forsingle speed systems, optimal efficiency is obtained for zones that areapproximately ⅓ of the load. When individual zones approach 20% of theload, it more efficient to switch to a variable speed system, althoughit is possible to apply the control system of the invention to systemsthat includes zones with less than 20% of the airflow by including abypass to handle excess air. The allowable bypass airflow should be lessthan 12% of the blower output (typically expressed in cubic feet perminute or CFM) when the zone with the smallest CFM requirement isoperating.

Control of airflow can be achieved using a conventional, commerciallyavailable multiple-zone HVAC controller. The controller typicallyincludes a processor, a programming interface, a memory for storing thecontrol sequence, and an interface that allows connections to thecentral HVAC unit, temperature sensors or thermostats, and individualdiffusers or dampers to control airflow in individual zones. Theconnections may be standard wired connections and/or wireless/networkconnections.

Other than modified programming as described above, the onlymodification required to implement the method and system of thepreferred embodiments is enlargement of duct and/or diffuser openingsizes to accommodate increased airflow. An example of the manner inwhich ducts sizes are enlarged is included in FIGS. 3-5, which showtables comparing standard ducts in an exemplary three zone HVAC systemwith ducts that are modified in accordance with the principles of theinvention.

The central HVAC unit in the example of FIGS. 3-5 has an output of 600CFM. When the airflow is allocated in conventional fashion, theallocation is such that zone 1 is designed to receive a maximum of 249CFM, zone 2 to receive 226 CFM, and zone 3 to receive 223 CFM, which isthe total of the first numerical column in each table labeled as DuctDesign CFM J8. The designation “J8” refers to calculations in thepublication Manual J Duct Design CFM. Each of the entries represents apercentage of the 249 CFM total, based on room size and diffuser throwand spread.

The third numerical column in each of the tables included in FIGS. 3-5for the three zones represents CFM values for the enlarged ducts of thepreferred embodiments of the invention. Instead of the J8 calculations,the duct sizes in column 3 are, based on the formulas:

Zone CFM=Total CFM−Minimum CFM  (1)

Duct CFM=Zone CFM×Percentage  (2)

The variable “Zone CFM” represents the maximum airflow that is allocatedto the initial calling zone, as described above. The variable “TotalCFM” is the total output of the central HVAC unit that is available tothe zone. The variable “Duct CFM” is based on a percentage of the ZoneCFM based on the percentage of total Zone CFM that is distributed toeach duct in the zone. The “Percentage” value is a function of duct anddiffuser geometry and may be calculated by standard methods based onroom size and required diffuser throw and spread, as set forth in ManualJ. These percentage calculations for relative sizes of ducts within azone are unaffected by and form no part of the present invention.Finally, the variable “Minimum CFM” is the minimum percentage that needsto be allocated to other zones. “Minimum CFM” may be calculated in avariety of ways but, in the example given in the tables is calculated bysubtracting the conventional J8 value from the total CFM and multiplyingthe result by 10%:

Minimum CFM=(Total CFM−J8 Value)×0.1  (3)

Both the percentage 0.1 and the J8 value may be varied depending onhealth and safety needs.

It can be understood from the above calculations and the results shownin FIGS. 3-5 that the airflow capacities of the ducts in the examplesdiffer substantially from standard duct airflows designed according tothe J8 manual. For example, the diffusers labeled Kitchen 1 and Kitchen2 in the first zone example shown in FIG. 3 are each increased in sizeto handle 102 CFM rather than 45 CFM, and the total zone CFM hasincreased from 249 CFM to 564.9 CFM. Of course, these values areexemplary in nature only and will vary depending on actual room and zoneconfigurations. The specific room configuration for the values in Tables3-5 is illustrated in FIG. 6.

For two speed systems, the duct design can be based on low speed CFMfull flow capacities. The system would only be permitted to operate athigher speed when a second zone is opened or when one zone is designedto take more than 50% of the airflow, taking into account supply ductstatic pressure. Similar design considerations apply for multiple orvariable speed systems, with the system designed to provide full flow toonly one zone during low speed operation, and higher speeds permittedwhen more than zone is calling. Although this may result in less thanfull flow allocation to a zone, the airflow allocation will still behigher than for the calculated Manual J8 or other conventionallycalculated loads.

In addition to increased CFM requirements for diffusers, those skilledin the art will appreciate that the return outlet and duct capacitiesmust be increased accordingly. Other than increase airflow handlingrequirements, however, the system of the invention does not require anyadditional hardware and may utilize existing controller hardware,programmed to control the airflow in the manner described in connectionwith FIGS. 1 and 2, and to include the predetermined minimum airflowstop setting.

Finally, it is to be understood that the above embodiments are intendedto illustrate the principles of the invention, and that the scope of theinvention is defined by the appended claims. Variations andmodifications of the preferred embodiments may be made without departingfrom the scope of the invention.

I claim:
 1. A method of controlling airflow in a multiple zoneheating/air conditioning system, comprising the steps of: monitoringindividual zone temperature control sensors by a controller, and when asensor in a first calling zone sends a signal indicating that atemperature in the first calling zone is above or below a set point by apredetermined amount, operating a heating or cooling unit to heat orcool air and supplying the heated or cooled air to diffusers in thefirst calling zone via ducts, wherein the first calling zone isallocated all of the airflow output by the heating or cooling unitexcept for a predetermined minimum airflow output that is allocated toall other zones; maintaining allocation of all of the airflow output tothe first calling zone except for the predetermined minimum airflowoutput and preventing more than the predetermined minimum airflow outputfrom being allocated to all other calling zones until the temperature inthe first calling zone reaches a desired temperature.
 2. A method ofcontrolling airflow in a multiple zone heating/air conditioning systemas claimed in claim 1, further comprising the step of terminating theallocation of all of the airflow output except for the predeterminedminimum airflow output to the first calling zone and instead supplyingall of the airflow output except for the predetermined minimum airflowoutput to a second calling zone when the second calling zone has apriority that is higher than a priority of the first calling zone.
 3. Amethod of controlling airflow in a multiple zone heating/airconditioning system as claimed in claim 1, further comprising the stepof terminating the allocation of all of the airflow output except forthe predetermined minimum airflow output to the first calling zone andinstead supplying all of the airflow output except for the predeterminedminimum airflow output to a second calling zone when a temperature inthe second calling zone deviates by a greater amount from a set point inthe second calling zone than the temperature in the first calling zonedeviates from the set point in the first calling zone.
 4. A method ofcontrolling airflow in a multiple zone heating/air conditioning systemas claimed in 1, further comprising a step of delaying restart of thecondenser after the temperature of the first calling zone has reached apredetermined temperature and no other zone has called.
 5. A multiplezone heating and air conditioning system, wherein ducts and diffusers inrespective zones of the multiple zone heating and air conditioningsystem are configured to accommodate an enlarged air flow calculatedbased on the formula:Zone CFM=Total CFM−Minimum CFM  (1) where “Zone CFM” is an airflowallocated by a central controller to the zone, “Total CFM” is a totaloutput of a central heating and/or air conditioning unit, and “MinimumCFM” is a minimum airflow distributed to other zones to ensure minimumadequate ventilation.
 6. A multiple zone heating and air conditioningsystem as claimed in claim 5, wherein the minimum airflow isapproximately 10% of “Total CFM.”
 7. A multiple zone heating and airconditioning system as claimed in claim 5, comprising a plurality ofdiffusers and temperature control sensors with user-established setpoints in each zone, the diffusers being opened and closed by a centralcontroller, wherein the central controller is programmed to executeinstructions for controlling opening and closing of the ducts accordingto the following sequence of steps: monitoring the zone temperaturecontrol sensors, and when a sensor in a first calling zone sends asignal indicating that a temperature in the first calling zone is aboveor below a set point by a predetermined amount, operating a heating orcooling unit to heat or cool air and supplying the heated or cooled airto diffusers in the first calling zone via ducts, wherein the firstcalling zone is allocated all of the airflow output by the heating orcooling unit except for the minimum airflow that is distributed to theother zones.
 8. A multiple zone heating and air conditioning system asclaimed in claim 7, wherein the controller is further programmed toexecute instructions for terminating the allocation of all of theairflow output except for the minimum airflow to the first calling zoneand supplying all of the airflow output except for the minimum airflowto a second calling zone when the second calling zone has a prioritythat is higher than a priority of the first calling zone.
 9. A multiplezone heating and air conditioning system as claimed in claim 7, whereinthe controller is further programmed to execute instructions forterminating the allocation of all of the airflow output except for thepredetermined minimum airflow output to the first calling zone andinstead supplying all of the airflow output except for the predeterminedminimum airflow output to a second calling zone when a temperature inthe second calling zone deviates by a greater amount from a set point inthe second calling zone than the temperature in the first calling zonedeviates from the set point in the first calling zone.
 10. A multiplezone heating and air conditioning system as claimed in claim 7, whereinthe controller is further programmed to execute instructions fordelaying restart of the condenser after the temperature of the firstcalling zone has reached a predetermined temperature and no other zonehas called.